The present invention relates, in general, to an electrostatographic image forming apparatus, and more specifically, to a system for cleaning of residual toner, dirt particles, and other debris from or for preventing contamination of a charge retentive belt or drum surface of an image forming or holding electrophotographic imaging member.
In electrophotographic imaging applications such as xerography, a charge retentive photoreceptor belt or drum is electrostatically charged according to the image to be produced. In a digital printer, an input device such as a raster output scanner controlled by an electronic subsystem can be adapted to receive signals from a computer and to transpose these signals into suitable signals so as to record an electrostatic latent image corresponding to the document to be reproduced on the photoreceptor. In a digital copier, an input device such as a raster input scanner controlled by an electronic subsystem can be adapted to provide an electrostatic latent image to the photoreceptor. In a light lens copier, the photoreceptor may be exposed to a pattern of light from an original image to be reproduced. In each case, the resulting pattern of charged and discharged areas on photoreceptor form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image.
The electrostatic image on the photoreceptor may be developed by contacting it with a finely divided electrostatically attractable toner. The toner is held in position on the photoreceptor image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original beam reproduced. Once each toner image is transferred to a substrate, the image is affixed thereto form a permanent record of the image to be reproduced. In the case of multicolor copiers and printers, the complexity of the image transfer process is compounded, as four or more colors of toner may be transferred to each substrate sheet. Once the single or multicolored toner is transferred to the substrate, it is permanently affixed to the substrate sheet by fusing so as to create the single or multicolor copy or print.
Subsequent to the photoreceptor to substrate toner transfer process, it is necessary to at least periodically clean the charge retentive surface of the photoreceptor. In order to obtain the highest quality copy or print image, it is generally desirable to clean the photoreceptor surface each time after the toner image is transferred to a substrate or receiving member. In addition, other particles such as paper fibers, dirt debris, toner additives and other impurities (hereinafter collectively referred to as "residue") may remain on the charged surface of the photoreceptor after transfer. Cleaning blades and brushes may be employed to remove residue from a photoreceptor surface. Typical polymeric materials used for cleaning blade application include thermoplastic and thermoset polyurethane elastomers, silicones, polybutadiene, vitons, polyphosphazines, polyvinyl chlorides, polyacrylates, polycarbonates, and the like. In practice, an elastomeric polyurethane blade is generally preferred and used to scrape debris residue from the photoreceptor surface. A rotating cleaning brush, may also be used to remove, loosen, dislodge, abrade or otherwise clean unwanted toner and other residue from the photoreceptor surface.
When using a cleaning blade of polymeric material, such as an elastomeric polyurethane blade to clean residue toner particles and debris from the surface of an organic photoreceptor belt or drum, a fraction of the corona species emitted from the photoreceptor charging device has been found to be adsorbed by the blade during the electrophotographic imaging process. These corona species outgas from the blade matrix during the period when the imaging machine is idled. This outgassing of corona species causes a variety of problems, such as copy deletion print defects originating at the location on the photoreceptor where the blade previously rested on the surface of the photoreceptor. This copy deletion print defect problem includes visible inboard-outboard transverse defect lines in copies and prints corresponding to the exact location where the blade and photoreceptor were in intimate contact during the period when the machine was in idle. Prior art solutions have included the use of a mechanical system to retract the cleaning blade away from the photoreceptor surface when the machine is in idle in order to prevent the blade and photoreceptor from remaining in contact. This retraction of the cleaning blade eliminates the cause of chemical attacks by out-gassing of corona species which degrade the photoreceptor. Such blade retraction mechanisms can add costs and complexity to the imaging system and may also create new problems. Thus, it is desirable to avoid using a blade retraction system and focus on an approach which can not only reduce manufacturing costs, but also eliminate the frequent need of service call and repair requirements associated with using such a device. Unfortunately, elimination of such a blade retraction system can lead to an undesirable residue spots printout problem that can be observed on final copies.
During xerographic imaging and cleaning processes, it has been found that the elastomeric cleaning blade polymer matrix absorbs and cumulatively stores a substantial amount of corona species discharged from the charging devices. Similarly, when intermediate transfer members (drums or belts) are used in an electrostatographic imaging process, they may also be affected by the corona species. Any device proximate to or in periodic or continuous contact with an imaging member (such as a bias transfer roll, a plastic housing used for cleaning or some other purpose) may contribute to degradation of an image forming or holding member. Such devices include intermediate transfer members and bias transfer members. Intermediate transfer members and bias transfer members are well known and described, for example, in U.S. Pat. No. 5,119,140, the entire disclosure thereof being incorporated herein by reference.
The corona species may be emitted from high voltage charging devices such as corotrons and scorotrons. The corona species absorbed by the cleaning blade can subsequently outgas from the cleaning blade and chemically attack the electrically active components in the photoreceptor. This attack may occur at the location where blade tip/edge and photoreceptor surface are in prolonged intimate contact thereby causing repetitive development of narrow areas of print defect corresponding to the chemically damaged regions of the photoreceptor. The print defects are manifested as deletion bands or solid line defects on printout copies, depending on the development system employed in the copier or printer. The damage to the photoreceptor can be long lived and even may be permanent. Generally, the only way to correct this problem is by costly outright replacement of both the photoreceptor and the cleaning blade. In some cases, the copy print defect may appear only after a few thousand copies. Therefore, for a photoreceptor having a long projected target life, such a premature failure represents an unacceptable major component life setback.
Attempts to resolve the corona species chemical attack issue have been proposed and tested over the years. Although antioxidant cleaning blade impregnation has been disclosed, the described process involves antioxidant impregnation of the blade by swelling and deswelling a blade in a thermodynamically good solvent containing dissolved antioxidant. This impregnation process is cumbersome, costly, slow and undesirable for production implementation. Moreover, the swelling/deswelling process involves large volumes of organic solvent waste which require safe disposal. Still another disadvantage noted during the deswelling step carried out in air ambient was that rapid solvent evaporation from the blade surface often created large instantaneous tension stress at the blade surface due to contraction caused by quick lost of solvent which led to cracking and fracture of the blade.